A wide variety of apparatus and methods are known in the art for the provision of cooked cereal doughs, especially for ready-to-eat (RTE) cereal products. Such apparatus and methods convert a raw dry ungelatinized cereal material and water into a cooked cereal dough characterized by hydration and gelatinization of the starchy constituents of the cereal material. Important aspects of cereal cooking include not only the degree of gelatinization but also the texture of the cooked cereal dough.
A well known cereal cooking apparatus is known in the art as a James Cooker. The James Cooker provides a low shear, low pressure, extended time (e.g., 30 to 180 minutes) type of cooking yielding a cooked cereal dough that has a highly developed cooked flavor but has not experienced high amounts of shear. The dough is extruded under low shear through die plates with die holes to produce sized and shaped cooked cereal dough pellets. The basic design and operation of the James Cooker is described in U.S. Pat. Nos. 2,233,919 (issued Mar. 4, 1941 to T. R. James), 2,263,301 (issued Nov. 18, 1941 to T. R. James), and 2,272,007 (issued Feb. 3, 1942 to T. R. James), each of which is incorporated herein by reference. Over the years, various improvements have been made to the James Cooker (see, for example, U.S. Pat. No. 5,433,490, issued Jul. 18, 1995 to R. Hurd and S. Liedman which describes a quick change die mechanism especially useful for the James Cooker for the rapid change outs of plugged dies, also incorporated by reference herein).
The present invention provides further improvements in the James Cooker, namely; reductions in downtime, improvements in throughputs, and improvements in cook consistency and degree of control. The present invention involves mounting a twin screw preconditioning unit onto the inlet of the James Cooker for mixing, hydrating, heating and converting a cereal feed material into precooked crumbly dough material prior to feeding into the James Cooker.
James Cookers are typically run 24 hours a day in product runs from seven up to 21 or more days. During such extended production runs, however, the cookers frequently require being brought temporarily off-line due to plugging of the dies. Fouling or even plugging of the dies is most frequently caused by dry, hard dough balls in which the cereal material is incompletely cooked due to incomplete hydration of the cereal material. Changing out the die can require several hours before a clean die is in place and the cooker is brought up to steady state conditions. Such die change outs are required at unpredictable intervals and may happen several times a day. Also, a great quantity of food material that is inconsistently processed before the cookers reach steady state conditions must be discarded. In the '490 patent, this problem was addressed by an improvement in the outlet end of the James Cooker, namely, by providing a faster means for changing out the plugged dies.
However, the present invention provides an improvement in the inlet end of the James Cooker. Specifically, the present invention resides in part in adding a particular twin screw preconditioning unit. By adding the present twin screw preconditioning unit, improvements are obtained in the consistency of hydration of the cereal feed material. Such hydration consistency improvements lead to reductions in the incidence of die plugging from dry dough balls. Reductions in downtime alone and attendant material waste represent significant cost savings, especially over extended production runs. The present invention can be used alone or in combination with the quick die changer improvements described in the '490 patent.
Such further reductions in downtime due to fewer plugged dies provided by the twin screw preconditioning unit alone can result in productivity improvements of 10 to 20%.
In addition to reducing downtime, employment of a twin screw preconditioning unit increases significantly the throughput of such James Cookers. Conceptually, the James Cooker has three zones in its cooking section that 1) mixes the ingredients, 2) hydrates the mixture, and 3) cooks the hydrated mixture. In addition to its cooking section, the James Cooker also includes a working section that works the cooked cereal material into a dough and extrudes the dough through the die plate to form cooked cereal dough pellets. The twin screw preconditioning unit performs the functions previously performed in the first two zones of cooking section of the James Cooker allowing for a more rapid and thus higher throughput of cereal material. The improvements in throughput can range from 10 to 25%.
By both reducing downtime and by increasing throughput, the total increase in output can be from about 20 to 45% or even more. In view of the expense of such James Cookers, such increases in output lead to dramatic cost savings and increased productivity.
Of course, rotating paddle types of cereal preconditioners are known for use immediately upstream of high shear extruders (see for example, U.S. Pat. No. 5,120,559, issued Jun. 9, 1992 to S. H. Rizvi, U.S. Pat. No. 4,285,271, issued Aug. 25, 1981 to Falck et al; and/or U.S. Pat. No. 4,665,810, issued May 19, 1987 to Falck). However, such preconditioners generally involve the mere passive exposure to wet moist steam to accomplish hydration. Also, the output material from such preconditioners must necessarily be free flowing, granular and fluffy in order to feed the material to single or twin screw extruders, in contrast to the more dense compacted precooked cereal dough material that exits the twin screw preconditioning unit of the present invention.
Still another advantage of the present invention resides in the ability to control the consistency of the cooked dough with respect to both texture and flavor. Moreover, conventional cereal preconditioners, and even prior usage of the James Cooker, typically require close control of the particle size of the cereal material. Since such preconditioners and the James Cooker passively expose the material to wet steam, close attention to the surface area-to-volume ratio must be made to ensure proper hydration. In contrast, using the present twin screw preconditioning unit allows for employment of a wide variety of particle size feed materials without materially adversely affecting the ability to control the desired cooked dough's properties.
Similarly, the consistency of hydration of the cereal mixture by using the twin screw preconditioning unit also results in a more consistent cook in the James Cooker in addition to the reduction in the incidence of die plugging. A more consistent cook results in a gain in product quality and may result in enhanced flavor development in the dough which was not previously possible with the James Cooker alone. The degree of hydration obtained independent of particle size, the more consistent cook, and the other attributes resulting in the utilization of the twin screw preconditioning unit with the James Cooker reduce the variability of the operating parameters and lend to automatic control to further simplify operator interface in the preparation of cooked cereal doughs.
Improved methods for preparing cooked cereal doughs having special application in the production of RTE cereals according to the preferred teachings of the present invention will become clearer in light of the following detailed description of an illustrative embodiment of this invention described in connection with the drawings.